Traffic related nitrogen oxide emissions have been vastly underestimated

Researchers from the EU-funded ALP-AIR project recently published findings from their continuous monitoring of trace gases concentrations in air. The team used the atmospheric measurement method called ‘eddy-covariance’ which applies statistical analyses to source data, inferring emissions within a radius of about one kilometre of the measurement location.

The study published in ''Scientific Reports'' was based on measurements conducted in 2015 over three months in Innsbruck, Austria. The findings show that nitrogen oxide concentrations came mainly from two human activities, namely road traffic and residential combustion. Over 80% was contributed by traffic, with the majority caused by diesel cars.

Redressing the balance of under-estimated nitrogen oxide emissions

From their urban observatory, the ALP-AIR team recorded carbon dioxide (CO2), nitrogen oxide (NO) and volatile organic compounds (VOCs) at the level of 36 000 data points per hour. ‘This result is relatively representative for the whole city,’ says Dr Thomas Karl from the Institute of Atmospheric and Cryospheric Sciences at the University of Innsbruck. Speaking about the relevance of the results in highlighting the limitations of alternative approaches he goes on the to say that, ‘Even newer atmospheric models are based on emission inventories that underestimate nitrogen oxide emission levels up to a factor of four.’

Levels of nitrogen oxide regularly exceed the maximum permissible in urban areas across Europe. Part of being able to address this challenge requires that sources be accurately identified and measured. However, most policies to manage air pollution are based on atmospheric modelling with experimental data from test facilities. As the recent diesel emissions scandal amply demonstrated, measurements acquired at engine test stands bear little relation to actual environmental impacts.

It is precisely this in-situ provenance of the ALP-AIR data-set that makes the research especially valuable. Significantly, the study also found evidence that breaches of EU safety limits for NO, were no longer limited to metropolitan, industrialised areas but also prevalent in smaller locations, making the findings especially timely. The ALP-AIR researchers refer to the study site of Innsbruck, which is a major vehicle crossing point between Northern and Southern Europe with around six million vehicles passing through each year, as representative of Central Europe and the greater Alpine region.

Towards better air pollution and health management

In the twentieth century, rapid industrialisation, alongside agricultural practices to increase yield, for example with the use of synthetic fertilisers, led to a significant increase of atmospheric NO. In higher concentrations NO is toxic and classified as a hazardous air pollutant, linked to health problems, such as breathing difficulties, as well as being a major contributor to ground-level ozone pollution, with its knock on climate impacts.

Shifting to diesel powered cars while resulting in reduced CO2 emissions through better fuel economy, has had the consequence of increasing NO emissions across Europe. As the study points out, with growth in the uptake of diesel-fulled vehicles is set to rise by 70%, with Asia being a key area for the increase, there is a pressing need for a better understanding of NO changes and ozone chemistry for accurate environment impact assessments.

Chief amongst the project’s aims were the development of comprehensive new tools for environmental monitoring, as well as a direct contribution to improved Earth system models. Looking to the future, in addition to extending the emissions monitoring time-period, the researchers also intend to investigate the impact of motorways, seasonality and agricultural activities on emissions.

For more information, please see:
CORDIS project webpage